CN114351358A - ePTFE-TPU composite membrane and preparation method thereof - Google Patents
ePTFE-TPU composite membrane and preparation method thereof Download PDFInfo
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Abstract
The invention relates to the technical field of ePTFE-TPU composite membranes, in particular to an ePTFE-TPU composite membrane and a preparation method thereof. The preparation method of the ePTFE-TPU composite membrane comprises the following steps: and spinning the TPU spinning solution by using an electrostatic spinning process to spin the TPU membrane on the ePTFE membrane. The preparation method can improve the problem of interfacial bonding of materials with extremely large surface energy difference between the ePTFE membrane and the TPU membrane on the basis of not needing an adhesion process, and meanwhile, the composite membrane also has the advantages of good adhesion, creep resistance, high elastic recovery rate, water resistance, moisture permeability and good air permeability.
Description
Technical Field
The invention relates to the technical field of ePTFE-TPU composite membranes, in particular to an ePTFE-TPU composite membrane and a preparation method thereof.
Background
The Polytetrafluoroethylene (PTFE) has excellent chemical stability, chemical corrosion resistance, weather resistance, high lubrication, non-adhesion, excellent biocompatibility, no toxicity, electric insulation, no dust and other excellent performances due to the unique molecular structure, and has wide temperature resistance, and can be used for a long time at the temperature of between 180 ℃ below zero and 260 ℃. This is difficult to achieve with any other polymer material, so it is known in the industry as "plastic king". PTFE microporous membranes (ePTFE) were originally developed by gore, usa and were produced by a solid-phase expansion molding method in which PTFE dispersion resin is subjected to a series of mechanical stretching operations such as extrusion, calendering, and stretching to draw out crystalline molecules from powdery particles to form fibers, and the fibers are interwoven to form a network structure. Besides maintaining all the properties of the PTFE, the ePTFE also has the effects of small aperture, uniform aperture distribution, high porosity, high film strength, water resistance, air permeability, dust prevention, wind resistance and heat preservation. Therefore, ePTFE has wide application in the fields of textile fabrics, cables, cable components, electronic elements, electrochemical materials, fiber products, filtration products, medical products, sealing products and the like.
After the ePTFE membrane is deformed by external force (especially under the condition of large deformation), the deformation is mainly retained in the form of plastic deformation, the creep is large, the elastic recovery rate is low, and particularly in the field of textile fabrics, such as a collar of a pullover is large, and elbows of sleeves and knees of trousers are raised, so that the original pore structure and shape of the ePTFE membrane are damaged, the service life of the membrane is influenced, and therefore, the ePTFE membrane needs to be endowed with high elastic recovery rate on the basis of keeping the original performance of the ePTFE membrane.
Thermoplastic Polyurethane (TPU) refers to a class of polymeric synthetic materials that contain urethane groups in their molecular structure and have properties intermediate between those of rubber and plastic. The TPU has the characteristics of wear resistance, good flexibility and high elasticity, and has high permselectivity. If the ePTFE membrane is compounded with the TPU with elasticity, the obtained composite material has the advantages of the ePTFE membrane and the TPU, and not only can be waterproof, moisture permeable, breathable and dustproof, but also can enable the composite material to have good elasticity. The Goll company in America disclosed that hydrophilic polyurethane was coated on one side of an ePTFE film in 80 s, so that the oil stain resistance of one side of the ePTFE film can be improved, but the air permeability of the film is sacrificed, the waterproof and air permeability of the ePTFE film needs to be improved, and particularly when the ePTFE film is applied to functional clothing, the performance of the ePTFE film still has room for improvement.
There are many prior art patents which employ a method of preparing an ePTFE/TPU elastic composite film, for example, chinese patent (application No. 201310053567.0) employs a polytetrafluoroethylene resin and a lubricating oil to prepare an ePTFE film through mixing, preforming, paste extrusion, calendering, drying, stretching, sintering, etc., and then prepares an ePTFE/TPU elastic composite film through polyurethane coating compounding. Although the obtained composite membrane has good waterproof performance, the TPU side has no micropores, so that the composite membrane has no air permeability and no oleophobicity (only resisting No. 1 oil), and the composite fabric has poor moisture permeability and is uncomfortable to wear. In Chinese patent (application No. 201510181965.X), zinc chloride is dissolved in polyurethane coating liquid containing dimethyl formamide and ethyl acetate, the coating liquid is coated on one side of a polytetrafluoroethylene microporous membrane, the zinc chloride forms particles after the solvent is volatilized and is retained in a polyurethane film, the composite film is soaked in a water tank filled with tap water at a certain speed after being wound, and the zinc chloride is gradually dissolved in the water to form the coating microporous composite film. However, since the TPU has a small pore size and a low porosity, the permeability is not high although the moisture permeability is improved.
Although the invention can prepare the ePTFE composite film with elasticity, water resistance, moisture permeability and air permeability, the surface energy difference between the TPU film and the ePTFE film is extremely large, so that the problem of large adhesion exists, the problem caused by the large surface energy difference between the TPU film and the ePTFE film cannot be solved well even if the composite film prepared by adopting a coating mode is adopted, and meanwhile, no micropores (or too small pore diameter and too low porosity) are detected in the formed composite film, so that the moisture permeability and air permeability of the composite film are poor, and the performance needs to be further improved.
In view of this, the invention is particularly proposed.
Disclosure of Invention
The invention aims to provide an ePTFE-TPU composite membrane and a preparation method thereof. The preparation method can improve the problem of interfacial bonding of materials with extremely large surface energy difference between the ePTFE membrane and the TPU membrane on the basis of not needing an adhesion process, and meanwhile, the composite membrane also has the advantages of good adhesion, creep resistance, high elastic recovery rate, water resistance, moisture permeability and good air permeability.
The invention is realized by the following steps:
in a first aspect, the present invention provides a method for preparing an ePTFE-TPU composite membrane, comprising: and spinning the TPU spinning solution by using an electrostatic spinning process to spin the TPU membrane on the ePTFE membrane.
In an alternative embodiment, the method comprises the following steps: the ePTFE membrane is modified prior to spinning using an electrospinning process.
In an alternative embodiment, the step of modifying comprises: treating the ePTFE membrane with low-energy plasma;
preferably, the step of modifying treatment comprises: sequentially washing, drying and treating the ePTFE membrane by low-energy plasma;
preferably, the temperature for drying is 40-120 ℃;
preferably, the gas used for the low-energy plasma treatment includes at least one of nitrogen, air, helium, and oxygen;
preferably, the conditions of the low-energy plasma treatment include: the air pressure is 5-50Pa, the power is 50-400W, and the time is 0.5-10 min.
In an alternative embodiment, the conditions of the electrospinning process include: the voltage of electrostatic spinning is 10-30 KV; the receiving voltage is 1.5-2KV, and the receiving speed is 80-100 r/min; the receiving distance is 15-25 cm; the injection speed of electrostatic spinning is 0.1-0.2 mm/min; the translation speed is 400-600mm/min, and the moving distance is 100-200 mm.
In an alternative embodiment, the mass volume concentration of TPU in the TPU spinning dope is from 5 to 20%.
In an alternative embodiment, the preparation of the TPU spinning dope comprises: dissolving TPU in an organic solvent;
preferably, the organic solvent is a mixed solution of an amine solvent and a furan solvent;
preferably, the organic solvent is a mixed solution of N, N-dimethylformamide and tetrahydrofuran;
preferably, the volume ratio of the N, N-dimethylformamide to the tetrahydrofuran is 2:8 to 7: 3.
In an alternative embodiment, the method comprises the following steps: carrying out post-treatment after spinning by adopting an electrostatic spinning process;
preferably, the post-processing comprises: after spinning by adopting an electrostatic spinning process, drying and heat treatment are sequentially carried out;
preferably, the conditions of drying include: the temperature is 40-80 ℃, and the time is 12-36 h;
preferably, the conditions of the heat treatment include: the temperature is 150 ℃ and 160 ℃, and the time is 1-5 min.
In a second aspect, the present invention provides an ePTFE-TPU composite membrane prepared by the method of preparing an ePTFE-TPU composite membrane according to any one of the preceding embodiments.
In an alternative embodiment, the TPU membrane of the ePTFE-TPU composite membrane has a thickness of 20 to 45 microns.
In an optional embodiment, the ePTFE-TPU composite membrane has a peel strength of 2-4N/mm, a longitudinal elastic recovery rate of 80-95%, a transverse elastic recovery rate of 80-95%, and a moisture permeability of 5500g/m2/24h-6500g/m2And 24h, the hydrostatic pressure resistance is 100KPa-150 KPa.
The invention has the following beneficial effects: the embodiment of the invention forms the TPU membrane with high specific surface area and high porosity by electrostatic spinning, so that the ePTFE-TPU composite membrane has the advantages of two membranes simultaneously, and overcomes the defects of poor adhesion, large creep, low elastic recovery rate, low separation efficiency of a single-layer pore structure and the like of the ePTFE membrane. The prepared composite membrane not only has good cohesiveness and high elastic recovery rate, but also has the advantages of water resistance, moisture permeability and good air permeability. Meanwhile, the surface treatment of the ePTFE by adopting low-energy plasma can improve the surface tension of the membrane material under relatively mild irradiation energy, so that the TPU fiber obtained by electrostatic spinning can be well attached to the surface of the ePTFE membrane, and even can pass through the ePTFE micropores to be twisted with the fiber in the ePTFE membrane, and thus the two-layer membrane can have high peel strength without adopting any adhesive. The physical connection has the advantages that the through of micropores of the two layers of membranes can be well kept, and the whole membrane material can be endowed with good mechanical strength and elastic recovery capability.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is an electron microscope scan of the TPU surface of the ePTFE-TPU composite film provided in example 1 of the present invention;
FIG. 2 is an electron microscope scan of the TPU surface of the ePTFE-TPU composite film provided in example 2 of the present invention;
FIG. 3 is an electron microscope scan of the TPU surface of the ePTFE-TPU composite film provided in example 3 of the present invention;
FIG. 4 is an electron microscope scan of the TPU surface of the ePTFE-TPU composite film provided in example 4 of the present invention;
FIG. 5 is an electron microscope scan of the TPU surface of the ePTFE-TPU composite film provided in example 5 of the present invention;
FIG. 6 is an electron microscope scan of the TPU surface of the ePTFE-TPU composite film provided in example 6 of the present invention;
FIG. 7 is an electron microscope scan of the TPU surface of the ePTFE-TPU composite film provided in example 7 of the present invention;
FIG. 8 is an electron microscope scan of a cross section of an ePTFE-TPU composite membrane provided in comparative example 6 of the present invention;
FIG. 9 is an electron microscope scan of a TPU cross section of an ePTFE-TPU composite film provided in example 3 of the present invention;
FIG. 10 is a schematic view of the interfacial effect of the ePTFE-TPU composite membrane prepared according to the present invention;
FIG. 11 is a schematic view of the interfacial effect of ePTFE-TPU composite membrane prepared by direct coating;
FIG. 12 is a comparison of the microstructure of the ePTFE layer before stretching and after stretch recovery of the ePTFE-TPU composite membrane prepared in accordance with the present invention;
fig. 13 is a schematic representation of the deformation of the ePTFE layer during the stretch-recovery-stretch process of the ePTFE-TPU composite membrane made according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The embodiment of the invention provides a preparation method of an ePTFE-TPU composite membrane, which comprises the following steps:
s1, performing ePTFE membrane modification treatment;
the ePTFE membrane adopted in the embodiment of the invention is not a conventional polytetrafluoroethylene membrane, but an expanded polytetrafluoroethylene membrane prepared by a solid-phase expansion forming method, and the expanded polytetrafluoroethylene membrane has the effects of small pore diameter, uniform pore diameter distribution, high porosity, high membrane strength, water resistance, air permeability, dust prevention, wind prevention and warm keeping besides the characteristics of the polytetrafluoroethylene membrane. The ePTFE membrane used in the embodiments of the present invention is a commercially available membrane, such as ePTFE membrane for clothing from shandongsanrong new materials co.
Carrying out modification treatment on an ePTFE membrane by using plasma, specifically, taking an ePTFE membrane with a certain size, washing the ePTFE membrane with distilled water for 3-4 times, removing impurities on the surface of a sample, then placing the cleaned ePTFE membrane in a dryer for storage and drying, then placing the treated ePTFE membrane in a low-energy plasma treatment instrument from the dryer, vacuumizing, introducing required gas, waiting for 2min, and then adjusting to required air pressure; and adjusting the plasma processing power, and turning on the plasma processing for a certain time. The ePTFE membrane may be a uniaxially stretched membrane or a biaxially stretched membrane. The drying process is carried out in an oven, and the drying temperature is 40-120 ℃. The low-energy plasma processing gas is one or more of nitrogen, air, helium and oxygen. The pressure required by the low-energy plasma treatment is 5-50 Pa. The low-energy plasma processing power is 50-400W. The low-energy plasma treatment time is 0.5-10 min.
The ePTFE membrane treated by the low-energy plasma has good bonding capacity with a TPU membrane formed by subsequent electrostatic spinning, and after heat treatment, the bottom surface of the TPU layer is penetrated downwards with a plurality of penetration parts, each penetration part extends into the corresponding ePTFE membrane micropore and is fixedly connected with fibers in the ePTFE membrane, so that the mutual winding effect is formed after the penetration parts are connected with the ePTFE membrane micropores. If the TPU layer and the ePTFE thin film layer need to be peeled, and a permeation part and micropores need to be peeled, so that the peeling strength of the composite film is greatly improved, and the service life of the composite film is prolonged.
S2, preparing a TPU spinning solution;
dissolving TPU in an organic solvent; specifically, adding a certain amount of TPU particles into a mixed solution of N, N-Dimethylformamide (DMF) and Tetrahydrofuran (THF) in a certain proportion, sealing, mechanically stirring at normal temperature for a certain time to completely dissolve the TPU, preparing a spinning solution with a certain TPU content, and sealing for later use. The volume ratio of the N, N-Dimethylformamide (DMF) to the Tetrahydrofuran (THF) in the mixed solution is 2:8-7: 3. The proportion (w/v) of the TPU content in the TPU spinning solution is 5-20%.
S3, electrostatic spinning;
and (3) carrying out silk prevention on the TPU spinning solution by utilizing an electrostatic spinning process so as to spin on the ePTFE membrane to form the TPU membrane. Specifically, the TPU spinning solution prepared in S2 above was directly spun on the ePTFE membrane after the low energy plasma treatment in S1 above using an electrospinning device. The thickness of the TPU fiber layer is controlled by controlling the spinning time. The voltage of electrostatic spinning is 10-30 KV; the receiving voltage is 1.5-2KV, and the receiving speed is 80-100 r/min; the receiving distance is 15-25 cm; the injection speed of electrostatic spinning is 0.1-0.2 mm/min; the translation speed is 400-600mm/min, and the moving distance is 100-200 mm; the spinning time is 4-8 hours, and the thickness of the TPU film in the obtained ePTFE-TPU composite film is 20-45 microns.
The TPU membrane with high specific surface area and high porosity is formed by electrostatic spinning, so that the ePTFE-TPU composite membrane has the advantages of two membranes simultaneously, and the defects of poor adhesion, large creep, low elastic recovery rate, low separation efficiency of a single-layer pore structure and the like of the ePTFE membrane are overcome. The prepared composite membrane has the advantages of good cohesiveness, high elastic recovery rate, water resistance, moisture permeability and good air permeability. The microporous membrane composite material with high moisture permeability and super air permeability is more comfortable, the service life of the functional membrane is greatly prolonged, and the requirements of consumers are met to a greater extent.
S4, post-processing;
after spinning by adopting an electrostatic spinning process, drying and heat treatment are sequentially carried out; specifically, drying the crude product of the ePTFE-TPU composite membrane prepared by S3 in an oven at the drying temperature of 40-80 ℃ for 12-36 h. Fixing the dried composite membrane on an iron plate, and then carrying out heat treatment to obtain the final ePTFE-TPU composite membrane. The heat treatment process can be carried out in an oven or a sintering furnace with programmable temperature rise, the treatment temperature is 150-160 ℃, and the treatment time is 1-5 min.
Embodiments of the present invention provide an ePTFE-TPU composite membrane prepared by the method of preparing an ePTFE-TPU composite membrane according to any one of the preceding embodiments. The ePTFE-TPU composite membrane has the peel strength of 2-4N/mm, the longitudinal elastic recovery rate of 80-95 percent, the transverse elastic recovery rate of 80-95 percent, and the moisture permeability of 5500-6500g/m224h, the hydrostatic pressure resistance is 100-150 KPa.
It should be noted that the test method for peel strength provided by the examples of the present invention is described in GBT 2791-1995; the test method of the longitudinal and transverse elastic recovery rate is disclosed in FZT 70006-; see GBT 12704-91B for moisture permeability test methods; test methods for water resistance (hydrostatic pressure resistance) are described in GBT 4744-1997.
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
This example provides a method for preparing an ePTFE-TPU composite membrane, comprising:
washing the unidirectionally stretched ePTFE membrane with distilled water for 3-4 times to remove impurities on the surface of a sample, then placing the cleaned ePTFE membrane in an oven at 80 ℃ for 4 hours to remove moisture, then placing the cleaned and dried ePTFE membrane in a low-energy plasma processor, pumping to vacuum, introducing helium, waiting for 2 minutes, modulating the pressure of the helium by 20Pa, adjusting the low-energy plasma processing power to 350W, and opening the low-energy plasma for processing for 1 minute.
Secondly, preparing 15% (w/v) TPU spinning solution by taking a mixed solution (volume ratio of 1:1) containing DMF and THF as a solvent, and uniformly stirring at normal temperature (about 25 ℃) for later use. And (3) injecting the TPU spinning solution into a disposable injector with the capacity of 10mL, selecting a stainless steel needle with the specification of 23G, and adopting an electrostatic spinning device to directly perform electrostatic spinning on the TPU spinning solution on the ePTFE membrane treated by the low-energy plasma. The voltage of electrostatic spinning is 15KV, the receiving voltage is 2KV, and the receiving speed is 100 r/min; the receiving distance is 20 cm; the injection speed of electrostatic spinning is 0.125 mm/min; the translation speed is 500mm/min, and the moving distance is 200 mm; the spinning time was 4 hours.
Finally, the crude product of the ePTFE-TPU composite membrane prepared in the above way is dried in an oven at 80 ℃ for 4 hours to remove the solvent. Fixing the dried composite membrane on an iron plate, and performing heat treatment at 150 ℃ for 3min to obtain the final ePTFE-TPU composite membrane.
The TPU surface of the ePTFE-TPU composite film was observed by scanning electron microscopy (see FIG. 1). The thickness of the TPU film in the ePTFE-TPU composite film is 24 microns. The peeling strength of the ePTFE-TPU composite membrane reaches 3.42N/mm, the longitudinal and transverse elastic recovery rates are respectively 84.7 percent and 86.6 percent, and the moisture permeability is compared with that of a pure ePTFE membrane (5927 g/m)224h) is basically unchanged and reaches 5925g/m2And 24h, the hydrostatic pressure resistance is up to 108 KPa.
Example 2
This example provides a method for preparing an ePTFE-TPU composite membrane, comprising:
the electrospinning time was 6 hours, and the remaining operation and equipment were the same as in example 1. The thickness of the TPU film in the final ePTFE-TPU composite film was 38 μm, and the TPU surface was observed by scanning electron microscope (see FIG. 2). The peel strength of the ePTFE-TPU composite membrane is 3.51N/mm, the longitudinal and transverse elastic recovery rates are respectively 88.8 percent and 90.8 percent, and the moisture permeability is 5878g/m2And the hydrostatic pressure resistance is 117KPa for 24 h.
Example 3
This example provides a method for preparing an ePTFE-TPU composite membrane, comprising:
electrostatic spinningThe filament time was 8 hours and the remaining operating steps and equipment were as in example 1. The thickness of the TPU film in the final ePTFE-TPU composite film was 45 μm, and the TPU surface (see FIG. 3) and the cross section (see FIG. 9) were observed by a scanning electron microscope. The peel strength of the ePTFE-TPU composite membrane is 3.57N/mm, the longitudinal and transverse elastic recovery rates are respectively 92.3 percent and 94.0 percent, and the moisture permeability is 5812g/m2And the hydrostatic pressure resistance is 124KPa for 24 h.
Comparative example 1
The electrospinning time was 2 hours, and the remaining operation and equipment were the same as in example 1. The thickness of the TPU film in the finally obtained ePTFE-TPU composite film is 15 microns, the longitudinal and transverse elastic recovery rates of the obtained ePTFE film are only 44.9 percent and 43.4 percent respectively, and the moisture permeability is 5983g/m2And the hydrostatic pressure resistance is 99KPa for 24 h.
Comparative example 2
The electrospinning time was 10 hours, and the remaining operation and equipment were the same as in example 1. The thickness of the TPU film in the finally obtained ePTFE-TPU composite film is 50 microns, the longitudinal and transverse elastic recovery rates of the obtained ePTFE film are respectively 94.8 percent and 94.4 percent, and the moisture permeability is 4838g/m2And the hydrostatic pressure resistance is 132KPa for 24 h.
The above examples are compared with corresponding comparative examples to give the following table one.
TABLE one of the elastic recovery rates in the longitudinal and transverse directions, moisture vapor transmission rates, and hydrostatic pressure resistances of examples and comparative examples
As can be seen from table one, the thickness of the TPU layer significantly affects the longitudinal and transverse elastic recovery rate, moisture permeability and hydrostatic pressure resistance of the ePTFE-TPU membrane, and as the thickness of the TPU layer increases, the longitudinal and transverse elastic recovery rate and hydrostatic pressure resistance of the ePTFE-TPU composite membrane gradually increase, but at the same time, the moisture permeability also decreases significantly. Therefore, a proper thickness (20-45 μm) is required to ensure that the composite film has a good overall performance.
Example 4
This example provides a method for preparing an ePTFE-TPU composite membrane, comprising:
the concentration of the TPU electrostatic spinning solution is 10 percent, the rest steps are the same as the example 3, the thickness of a TPU film in the finally obtained ePTFE-TPU composite film is 45 micrometers, and the surface of the TPU is observed by a scanning electron microscope (shown in figure 4). Because the concentration of the spinning solution is low, a large number of spindles exist in TPU fibers, the peel strength of the ePTFE-TPU composite membrane is 3.45N/mm, and the moisture permeability is 5726g/m2And the hydrostatic pressure resistance is 129KPa for 24 h.
Example 5
This example provides a method for preparing an ePTFE-TPU composite membrane, comprising:
the concentration of the TPU electrostatic spinning solution is 20%, the rest steps are the same as the example 3, the thickness of the TPU film in the finally obtained ePTFE-TPU composite film is 45 micrometers, and the surface of the TPU is observed by a scanning electron microscope (see figure 5). The spinning solution has high concentration, increased viscosity, increased width of TPU fiber, peeling strength of 3.24N/mm, and moisture permeability of 5961g/m224h, the hydrostatic pressure resistance is 125KPa
Comparative example 3
The ePTFE-TPU composite membrane was prepared by a coating method, and the thickness of the TPU membrane in the finally obtained ePTFE-TPU composite membrane was 45 μm, with the rest of the steps being the same as in example 5. The moisture permeability of the ePTFE-TPU composite membrane is 3837g/m2And the hydrostatic pressure is 138KPa for 24 h.
The above examples are compared with corresponding comparative examples to give the following table two.
Hydrostatic pressure and moisture vapor transmission resistance of the second example and the comparative example
As can be seen from the hydrostatic pressure resistance and moisture permeability scales of the examples and the comparative examples, although the hydrostatic pressure resistance of the composite film prepared by the coating method is improved compared with the composite film prepared by electrospinning, the moisture permeability is greatly reduced. Therefore, the moisture permeability of the ePTFE-TPU composite membrane can be effectively improved through the electrostatic spinning mode.
Example 6
This example provides a method for preparing an ePTFE-TPU composite membrane, comprising:
the heat treatment time of the ePTFE-TPU composite membrane is 1min, the rest steps are the same as the example 3, and the TPU surface is observed by a scanning electron microscope (see figure 6). Because the heat treatment time is too short, the TPU layer and the ePTFE are not fully fused, the peel strength of the obtained ePTFE-TPU composite membrane is 1.14N/mm, and the longitudinal and transverse elastic recovery rates are 59.4 percent and 61.3 percent respectively; the moisture permeability is as high as 6064g/m2And 24h, the hydrostatic pressure resistance is up to 121 KPa.
Example 7
This example provides a method for preparing an ePTFE-TPU composite membrane, comprising:
the heat treatment time of the ePTFE-TPU composite membrane was 5min, and the rest of the procedure was the same as in example 3, and the TPU surface was observed by a scanning electron microscope (see FIG. 7). Because the heat treatment time is prolonged, the TPU layer and the ePTFE are fully fused, and the peel strength of the obtained ePTFE-TPU composite membrane is up to 3.62N/mm; the longitudinal and transverse strength of the composite membrane is respectively as high as 94.7% and 94.9%; because the heat treatment time is too long, the TPU fibers are mutually fused, so that the porosity of the composite film is reduced, and the moisture permeability of the composite film is as high as 5627g/m2And 24h, the hydrostatic pressure resistance is up to 134 KPa.
Comparative example 4
The heat treatment time of the ePTFE-TPU composite membrane is 0min, and the rest steps are the same as those of example 3. Because no heat treatment is carried out, the TPU layer and the ePTFE are not fused, the peel strength of the obtained ePTFE-TPU composite membrane is only 0.74N/mm, the longitudinal and transverse strength is 42.7 percent and 31.8 percent respectively, and the moisture permeability is 6018g/m2And the hydrostatic pressure resistance is 102KPa for 24 h.
Comparative example 5
The heat treatment time of the ePTFE-TPU composite membrane was 6min, and the rest of the procedure was the same as in example 3. Because the heat treatment time is too long, the fibers of the TPU layer are fused together to lose most of the pore structure, the peel strength of the obtained ePTFE-TPU composite membrane is 2.64N/mm, the longitudinal and transverse strength is 93.9 percent and 94.1 percent respectively, and the moisture permeability is 3518g/m2And the hydrostatic pressure resistance is 136KPa for 24 h.
The above examples are compared with corresponding comparative examples to give the following table three.
Peel Strength, elastic recovery in the longitudinal and transverse directions, moisture vapor Transmission and hydrostatic pressure resistance of the examples and comparative examples
As can be seen from the peel strength, the longitudinal and transverse elastic recovery rate, the moisture permeability, and the hydrostatic pressure resistance of the examples and comparative examples, the heat treatment can significantly improve the peel strength of the composite film, and the peel strength, the longitudinal and transverse elastic recovery rate, and the hydrostatic pressure resistance of the composite film are gradually reduced as the heat treatment time is increased. Therefore, proper heat treatment time (1-5min) is required to ensure that the composite film has better comprehensive performance
Example 8
This example provides a method for preparing an ePTFE-TPU composite membrane, comprising:
the helium plasma treatment time was set to 8min, and the procedure was the same as in example 3. The peel strength of the ePTFE-TPU composite membrane is 3.97N/mm, the longitudinal and transverse elastic recovery rates are 93.5 percent and 94.3 percent respectively, and the moisture permeability is 5880g/m2And the hydrostatic pressure resistance is 130KPa for 24 h.
Comparative example 6
The helium plasma treatment time was reduced to 0.4min, and the rest of the procedure was the same as in example 3. The peel strength of the ePTFE-TPU composite membrane is 1.65N/mm, the longitudinal and transverse elastic recovery rates are 63.1 percent and 67.3 percent respectively, and the moisture permeability is 5607g/m2And the hydrostatic pressure resistance is 125KPa for 24 h.
Comparative example 7
The helium plasma was reduced to 30W for the same process as in example 3. The peel strength of the ePTFE-TPU composite membrane is 1.13N/mm, the longitudinal and transverse elastic recovery rates are 59.0 percent and 61.3 percent respectively, and the moisture permeability is 5700g/m2And the hydrostatic pressure resistance is 127KPa for 24 h.
Comparative example 8
The helium plasma was ramped up to 800W for the remainder of the procedure as in example 3. The ePTFE-TPU composite membrane has a peel strength of 1.83N/mm, a longitudinal and transverse elastic recovery rate of 71.3% and 73.7%, respectively, and a moisture permeability of 5730g/m2And the hydrostatic pressure resistance is 124KPa for 24 h.
Comparative example 9
After helium plasma treatment is carried out on the surface of the ePTFE membrane by adopting the technical parameters of the embodiment 3, the TPU spinning solution prepared in the embodiment 3 is directly coated on the surface of the ePTFE membrane (namely, an electrostatic spinning mode is not adopted), and then the crude product of the prepared ePTFE-TPU composite membrane is dried in an oven at the temperature of 80 ℃ for 4 hours to remove the solvent. Fixing the dried composite membrane on an iron plate, and performing heat treatment at 150 ℃ for 3min to obtain a final ePTFE-TPU composite membrane, wherein the peel strength of the obtained ePTFE-TPU composite membrane is 1.98N/mm, the longitudinal and transverse elastic recovery rates are respectively 80.1% and 82.1%, and the moisture permeability is 2721g/m2And the hydrostatic pressure resistance is 208KPa for 24 h.
Comparative example 10
The gas used for the low energy plasma treatment of the ePTFE membrane was changed to air and the rest of the procedure was the same as in example 3. Because the treatment effect of air plasma treatment on the ePTFE membrane is not as good as that of helium, the obtained ePTFE-TPU composite membrane has the peel strength of 1.14N/mm, the longitudinal and transverse elastic recovery rates of 58.1 percent and 61.7 percent respectively, and the moisture permeability of 5827g/m2And the hydrostatic pressure resistance is 123KPa for 24 h.
Comparative example 11
The ePTFE membrane was not treated with low energy plasma and the remaining procedure was the same as in example 3. Because the interfacial compatibility between ePTFE and TPU is poor due to the fact that low-energy plasma treatment is not carried out, the cross section of the composite membrane is observed by a scanning electron microscope (see figure 8), and the peel strength of the obtained ePTFE-TPU composite membrane is small and is only 0.74N/mm.
Comparative example 12
The ePTFE membrane was not treated with low energy plasma, washed and dried, and then directly coated on the surface of the ePTFE membrane with the TPU spinning solution prepared in example 3, and then the crude ePTFE-TPU composite membrane prepared above was dried in an oven at 80 ℃ for 4h to remove the solvent. Fixing the dried composite membrane on an iron plate, and performing heat treatment at 150 ℃ for 3min to obtain a final ePTFE-TPU composite membrane, wherein the peel strength of the obtained ePTFE-TPU composite membrane is 1.03N/mm, the longitudinal and transverse elastic recovery rates are 66.5% and 66.7% respectively, and the moisture permeability is 2354g/m224h, hydrostatic pressure resistanceIs 204 KPa.
The above examples are compared with corresponding comparative examples to give the following table four.
TABLE IV Peel Strength of examples and comparative examples
As can be seen from the peel strength tables of the examples and comparative examples, after the low-energy plasma treatment, the surface hydrophilicity of the ePTFE is increased, so that TPU can be well spread on the ePTFE, and even part of TPU fibers can be intertwined with fibers in the ePTFE (see schematic diagram in fig. 10), so that the peel strength between the ePTFE and the TPU is remarkably improved. However, too low a treatment power or too short a treatment time of the helium plasma will result in a low peeling strength of the two layers due to insufficient irradiation, while too high a treatment power will result in a breakage of molecular chains in part of ePTFE due to excessive irradiation energy, which will also result in a low peeling strength. In addition, experiments prove that the enhancement effect of the helium plasma treatment on the peeling strength of the composite film is obviously better than the treatment effect of air plasma, but both effects are better than the situation without plasma treatment. On the other hand, the peel strength of the composite film material prepared by the direct coating method on the surface of the ePTFE membrane is lower than that of the composite film material prepared by the electrostatic spinning coating of TPU, because the directly coated TPU is only spread and attached on the surface of the ePTFE membrane and does not physically entangle with fibers in the ePTFE (see schematic diagram in fig. 11), and thus the bonding force of the two layers is insufficient. And the TPU film formed by the direct coating method has lower porosity, so that the moisture permeability of the composite film is greatly reduced.
Further, in addition to the improvement in peel strength, it is also of interest that the ePTFE-TPU composite membranes prepared using the present technology have excellent elastic recovery, which can approach 95% at best. The elastic recovery rate of the single-layer ePTFE is less than 5%, and the elastic recovery rate of the composite membrane prepared by adopting other gas plasmas or direct coating is lower than 80% after the composite membrane is elastically recovered. Through research, the composite membrane provided by the embodiment of the invention has the advantages that due to the physical entanglement of the TPU layer and the ePTFE layer at the interface, after the composite membrane is stretched and recovered, the fibers in the ePTFE layer which is difficult to elastically recover fold under the forced traction of the TPU layer (as shown in figure 12) to form a similar fold structure, and can be freely unfolded and folded, so that the composite membrane macroscopically shows excellent elastic recovery performance (as shown in figure 13).
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A preparation method of an ePTFE-TPU composite membrane is characterized by comprising the following steps: and spinning the TPU spinning solution by using an electrostatic spinning process to spin the TPU membrane on the ePTFE membrane.
2. The method of claim 1, comprising: the ePTFE membrane is modified prior to spinning using an electrospinning process.
3. The method according to claim 2, wherein the step of modification treatment comprises: treating the ePTFE membrane with low-energy plasma;
preferably, the step of modifying treatment comprises: sequentially washing, drying and treating the ePTFE membrane by low-energy plasma;
preferably, the temperature for drying is 40-120 ℃;
preferably, the gas used for the low-energy plasma treatment includes at least one of nitrogen, air, helium, and oxygen;
preferably, the conditions of the low-energy plasma treatment include: the air pressure is 5-50Pa, the power is 50-400W, and the time is 0.5-10 min.
4. The method of claim 1, wherein the conditions of the electrospinning process include: the voltage of electrostatic spinning is 10-30 KV; the receiving voltage is 1.5-2KV, and the receiving speed is 80-100 r/min; the receiving distance is 15-25 cm; the injection speed of electrostatic spinning is 0.1-0.2 mm/min; the translation speed is 400-600mm/min, and the moving distance is 100-200 mm.
5. The production method according to claim 1, wherein the mass volume concentration of the TPU in the TPU spinning solution is 5 to 20%.
6. The preparation method according to claim 5, wherein the preparation step of the TPU spinning solution comprises: dissolving TPU in an organic solvent;
preferably, the organic solvent is a mixed solution of an amine solvent and a furan solvent;
preferably, the organic solvent is a mixed solution of N, N-dimethylformamide and tetrahydrofuran;
preferably, the volume ratio of the N, N-dimethylformamide to the tetrahydrofuran is 2:8 to 7: 3.
7. The method of claim 1, comprising: carrying out post-treatment after spinning by adopting an electrostatic spinning process;
preferably, the post-processing comprises: after spinning by adopting an electrostatic spinning process, drying and heat treatment are sequentially carried out;
preferably, the conditions of drying include: the temperature is 40-80 ℃, and the time is 12-36 h;
preferably, the conditions of the heat treatment include: the temperature is 150 ℃ and 160 ℃, and the time is 1-5 min.
8. An ePTFE-TPU composite membrane prepared by the process for preparing an ePTFE-TPU composite membrane according to any one of claims 1 to 7.
9. An ePTFE-TPU composite membrane according to claim 8 wherein the TPU membrane in said ePTFE-TPU composite membrane has a thickness of 20 to 45 microns.
10. An ePTFE-TPU composite membrane according to claim 8, characterized in that said ePTFE-TPU composite membrane has a peel strength of 2 to 4N/mm, a longitudinal elastic recovery of 80 to 95%, a transverse elastic recovery of 80 to 95%, and a moisture permeability of 5500g/m2/24h-6500g/m2And 24h, the hydrostatic pressure resistance is 100KPa-150 KPa.
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